Constraining motion vectors of groups of blocks

ABSTRACT

Aspects of the disclosure provide methods and apparatuses for video coding. In some examples, an apparatus includes processing circuitry that obtains motion information of a group of blocks in a picture from a coded video bitstream, the motion information indicating base motion vectors for the group of blocks, and the base motion vectors pointing to a reference picture in a prediction list. The processing circuitry determines a range of target motion vectors for the group of blocks along a particular coordinate direction according to the base motion vectors and a target difference, where, for any two motion vector within the range, a difference of integer-pixel parts thereof along the particular coordinate direction is equal to or less than the target difference. The processing circuitry further converts the base motion vectors into the target motion vectors according to the range for reconstructing samples of the group of blocks.

INCORPORATION BY REFERENCE

This application is a continuation of U.S. application Ser. No.17/458,680, filed on Aug. 27, 2021, which is a continuation of U.S.application Ser. No. 16/517,156, filed on Jul. 19, 2019, now U.S. Pat.No. 11,184,635, which claims the benefit of priority to U.S. ProvisionalApplication No. 62/725,927, “SUB-BLOCK MOTION VECTOR CONSTRAINTS” filedon Aug. 31, 2018; U.S. Provisional Application No. 62/734,987, “IMPROVEDSUB-BLOCK MOTION VECTOR CONSTRAINTS” filed on Sep. 21, 2018; and U.S.Provisional Application No. 62/788,838, “AFFINE MOTION VECTOR CLIPPING”filed on Jan. 5, 2019. The entire disclosures of the prior applicationsare hereby incorporated by reference in their entirety.

TECHNICAL FIELD

The present disclosure describes embodiments generally related to videocoding.

BACKGROUND

The background description provided herein is for the purpose ofgenerally presenting the context of the disclosure. Work of thepresently named inventors, to the extent the work is described in thisbackground section, as well as aspects of the description that may nototherwise qualify as prior art at the time of filing, are neitherexpressly nor impliedly admitted as prior art against the presentdisclosure.

Video coding and decoding can be performed using inter-pictureprediction with motion compensation. Uncompressed digital video caninclude a series of pictures, each picture having a spatial dimensionof, for example, 1920×1080 luminance samples and associated chrominancesamples. The series of pictures can have a fixed or variable picturerate (informally also known as frame rate), of, for example 60 picturesper second or 60 Hz. Uncompressed video has significant bitraterequirements. For example, 1080p60 4:2:0 video at 8 bit per sample(1920×1080 luminance sample resolution at 60 Hz frame rate) requiresclose to 1.5 Gbit/s bandwidth. An hour of such video requires more than600 GBytes of storage space.

One purpose of video coding and decoding can be the reduction ofredundancy in the input video signal, through compression. Compressioncan help reduce the aforementioned bandwidth or storage spacerequirements, in some cases by two orders of magnitude or more. Bothlossless and lossy compression, as well as a combination thereof can beemployed. Lossless compression refers to techniques where an exact copyof the original signal can be reconstructed from the compressed originalsignal. When using lossy compression, the reconstructed signal may notbe identical to the original signal, but the distortion between originaland reconstructed signals is small enough to make the reconstructedsignal useful for the intended application. In the case of video, lossycompression is widely employed. The amount of distortion tolerateddepends on the application; for example, users of certain consumerstreaming applications may tolerate higher distortion than users oftelevision distribution applications. The compression ratio achievablecan reflect that: higher allowable/tolerable distortion can yield highercompression ratios.

Motion compensation can be a lossy compression technique and can relateto techniques where a block of sample data from a previouslyreconstructed picture or part thereof (reference picture), after beingspatially shifted in a direction indicated by a motion vector (MVhenceforth), is used for the prediction of a newly reconstructed pictureor picture part. In some cases, the reference picture can be the same asthe picture currently under reconstruction. MVs can have two dimensionsX and Y, or three dimensions, the third being an indication of thereference picture in use (the latter, indirectly, can be a timedimension).

In some video compression techniques, an MV applicable to a certain areaof sample data can be predicted from other MVs, for example from thoserelated to another area of sample data spatially adjacent to the areaunder reconstruction, and preceding that MV in decoding order. Doing socan substantially reduce the amount of data required for coding the MV,thereby removing redundancy and increasing compression. MV predictioncan work effectively, for example, because when coding an input videosignal derived from a camera (known as natural video) there is astatistical likelihood that areas larger than the area to which a singleMV is applicable move in a similar direction and, therefore, can in somecases be predicted using a similar motion vector derived from MVs ofneighboring area. That results in the MV found for a given area to besimilar or the same as the MV predicted from the surrounding MVs, andthat in turn can be represented, after entropy coding, in a smallernumber of bits than what would be used if coding the MV directly. Insome cases, MV prediction can be an example of lossless compression of asignal (namely: the MVs) derived from the original signal (namely: thesample stream). In other cases, MV prediction itself can be lossy, forexample because of rounding errors when calculating a predictor fromseveral surrounding MVs.

Various MV prediction mechanisms are described in H.265/HEVC (ITU-T Rec.H.265, “High Efficiency Video Coding”, December 2016). Out of the manyMV prediction mechanisms that H.265 offers, described here is atechnique henceforth referred to as “spatial merge”.

Referring to FIG. 1 , a current block (101) comprises samples that havebeen found by the encoder during the motion search process to bepredictable from a previous block of the same size that has beenspatially shifted. Instead of coding that MV directly, the MV can bederived from metadata associated with one or more reference pictures,for example from the most recent (in decoding order) reference picture,using the MV associated with either one of five surrounding samples,denoted A0, A1, and B0, B1, B2 (102 through 106, respectively). InH.265, the MV prediction can use predictors from the same referencepicture that the neighboring block is using.

SUMMARY

Aspects of the disclosure provide methods and apparatuses for videoencoding/decoding. In some examples, an apparatus includes processingcircuitry that obtains motion information of a group of blocks in apicture from a coded video bitstream, the motion information indicatingbase motion vectors for the group of blocks, and the base motion vectorspointing to a first reference picture in a first prediction list. Theprocessing circuitry determines a first range of target motion vectorsfor the group of blocks along a first coordinate direction according tothe base motion vectors and a first target difference for the firstcoordinate direction, where, for any two motion vector within the firstrange, a difference of integer-pixel parts thereof along the firstcoordinate direction is equal to or less than the first targetdifference. The processing circuitry further converts the base motionvectors into the target motion vectors according to the first range, andgenerates reconstructed samples of the group of blocks for output basedon the target motion vectors.

In some embodiments, the group of blocks includes sub-blocks of a codingblock in the picture.

In some embodiments, the processing circuitry determines one of an upperbound value and a lower bound value of the first range according to oneor more base motion vectors for one or more particular blocks in thegroup of blocks, the one or more particular blocks corresponding to arespective one or more predetermined positions in the coding block. Theprocessing circuitry further determines the other one of the upper boundvalue and the lower bound value of the first range according to thedetermined one of the upper bound value and an integer-pixel portion ofthe lower bound value, the first target difference, and a precisionsetting of the target motion vectors. The pro processing circuitryconverts the base motion vectors into the target motion vectors byclipping a first value of another base motion vector, along the firstcoordinate direction, for another block in the group of blocks to thelower bound value when the first value is less than the lower boundvalue, and by clipping the first value to the upper bound value when thefirst value is greater than the upper bound value.

In some embodiments, the group of blocks includes four 4×4 sub-blockswithin a 8×8 block area in the picture.

In some embodiments, the one or more particular blocks consist of afirst block in the group of blocks according to a scanning order. Insome embodiments, the one or more particular blocks consist of first twoblocks in the group of blocks according to a scanning order.

In some embodiments, the one or more particular blocks include allblocks in the group of blocks. In some embodiments, the processingcircuitry determines the first range of the target motion vectors forthe group of blocks along the first coordinate direction by performingone of (i) determining the upper bound value of the first rangeaccording to a maximum value of the base motion vectors, along the firstcoordinate direction, for the group of blocks, and (ii) determining thelower bound value of the first range according to a minimum value of thebase motion vectors, along the first coordinate direction, for the groupof blocks.

In some embodiments, the processing circuitry determines the first rangeof the target motion vectors for the group of blocks along the firstcoordinate direction by determining a maximum value of the base motionvectors, along the first coordinate direction, for the group of blocks,and determining a minimum value of the base motion vectors, along thefirst coordinate direction, for the group of blocks. In someembodiments, the processing circuitry determines the first range of thetarget motion vectors for the group of blocks along the first coordinatedirection by, in response to a determination that a first differencebetween the minimum value and a first integer-pixel part of the minimumvalue is less than a second difference between the maximum value and asecond integer-pixel part of the maximum value, (i) determining thelower bound value of the first range according to the minimum value ofthe base motion vectors, and (ii) determining the upper bound value ofthe first range according to an integer-pixel portion of the determinedlower bound value, the first target difference, and a precision settingof the target motion vectors. In some embodiments, the processingcircuitry determines the first range of the target motion vectors forthe group of blocks along the first coordinate direction by, in responseto a determination that the first difference is not less than the seconddifference, (i) determining the upper bound value of the first rangeaccording to the maximum value of the base motion vectors, and (ii)determining the lower bound value of the first range according to aninteger-pixel portion of the determined upper bound value, the firsttarget difference, and the precision setting of the target motionvectors.

In some embodiments, the processing circuitry determines the firsttarget difference according to a size and a shape of the coding block.

In some embodiments, the processing circuitry determines the first rangeof the target motion vectors for the group of blocks along the firstcoordinate direction by determining one of an upper bound value and alower bound value of the first range according to the base motionvectors for the group of blocks, and determining the other one of theupper bound value and the lower bound value of the first range accordingto an integer-pixel portion of the determined one of the upper boundvalue and the lower bound value, the first target difference, and aprecision setting of the target motion vectors. In some embodiments, theprocessing circuitry converts the base motion vectors into the targetmotion vectors by keeping unchanged, regardless of the first range, atleast one of three motion vectors for three blocks that correspond to atop-left sub-block, a top-right sub-block, and a bottom-left sub-blockof the coding block in the picture, clipping a first value of anotherbase motion vector, along the first coordinate direction, for anotherblock in the group of blocks to the lower bound value in response to adetermination that the first value is less than the lower bound value,and clipping the first value to the upper bound value in response to adetermination that the first value is greater than the upper boundvalue.

In some embodiments, the processing circuitry further stores the basemotion vectors for the group of blocks in a motion filed as referenceinformation for a subsequent motion vector prediction process or asubsequent deblocking process.

In some embodiments, the first target difference is derived according toa video coding standard or signaled via the coded video bitstream. Insome embodiments, the first target difference ranges from 0 to 3 integerpixels.

In some embodiments, the processing circuitry further determines asecond range of the target motion vectors for the group of blocks alonga second coordinate direction according to the base motion vectors and asecond target difference for the second coordinate direction, the secondrange corresponding to limiting a difference of integer-pixel parts oftwo of the target motion vectors along the second coordinate directionto be equal to or less than the second target difference. The convertingthe base motion vectors into the target motion vectors can be performedaccording to the first range and the second range.

Aspects of the disclosure also provide a non-transitorycomputer-readable medium storing instructions which when executed by acomputer for video decoding cause the computer to perform the methodsfor video decoding.

BRIEF DESCRIPTION OF THE DRAWINGS

Further features, the nature, and various advantages of the disclosedsubject matter will be more apparent from the following detaileddescription and the accompanying drawings in which:

FIG. 1 is a schematic illustration of a current block and itssurrounding spatial merge candidates in one example.

FIG. 2 is a schematic illustration of a simplified block diagram of acommunication system (200) in accordance with an embodiment.

FIG. 3 is a schematic illustration of a simplified block diagram of acommunication system (300) in accordance with an embodiment.

FIG. 4 is a schematic illustration of a simplified block diagram of adecoder in accordance with an embodiment.

FIG. 5 is a schematic illustration of a simplified block diagram of anencoder in accordance with an embodiment.

FIG. 6 shows a block diagram of an encoder in accordance with anotherembodiment.

FIG. 7 shows a block diagram of a decoder in accordance with anotherembodiment.

FIG. 8 is a schematic illustration of spatial neighboring blocks thatcan be used to determine motion information for a current block using anaffine motion compensation method in accordance with an embodiment.

FIG. 9 is a schematic illustration of temporal reference blocks that canbe used to determine motion information for a current block using analternative temporal motion vector prediction method in accordance withone embodiment.

FIGS. 10A and 10B are schematics illustration of spatial neighboringblocks and a temporal neighboring block that can be used to determinemotion information for a current block using a planar motion vectorprediction method in accordance with an embodiment.

FIG. 11 is a flow chart outlining a process of reconstructing a group ofblocks based on target motion vectors that comply with a set ofconstraints in accordance with one embodiment.

FIG. 12 is a schematic illustration of a computer system in accordancewith an embodiment.

DETAILED DESCRIPTION OF EMBODIMENTS

FIG. 2 illustrates a simplified block diagram of a communication system(200) according to an embodiment of the present disclosure. Thecommunication system (200) includes a plurality of terminal devices thatcan communicate with each other, via, for example, a network (250). Forexample, the communication system (200) includes a first pair ofterminal devices (210) and (220) interconnected via the network (250).In the FIG. 2 example, the first pair of terminal devices (210) and(220) performs unidirectional transmission of data. For example, theterminal device (210) may code video data (e.g., a stream of videopictures that are captured by the terminal device (210)) fortransmission to the other terminal device (220) via the network (250).The encoded video data can be transmitted in the form of one or morecoded video bitstreams. The terminal device (220) may receive the codedvideo data from the network (250), decode the coded video data torecover the video pictures and display video pictures according to therecovered video data. Unidirectional data transmission may be common inmedia serving applications and the like.

In another example, the communication system (200) includes a secondpair of terminal devices (230) and (240) that performs bidirectionaltransmission of coded video data that may occur, for example, duringvideoconferencing. For bidirectional transmission of data, in anexample, each terminal device of the terminal devices (230) and (240)may code video data (e.g., a stream of video pictures that are capturedby the terminal device) for transmission to the other terminal device ofthe terminal devices (230) and (240) via the network (250). Eachterminal device of the terminal devices (230) and (240) also may receivethe coded video data transmitted by the other terminal device of theterminal devices (230) and (240), and may decode the coded video data torecover the video pictures and may display video pictures at anaccessible display device according to the recovered video data.

In the FIG. 2 example, the terminal devices (210), (220), (230) and(240) may be illustrated as servers, personal computers and smart phonesbut the principles of the present disclosure may be not so limited.Embodiments of the present disclosure find application with laptopcomputers, tablet computers, media players and/or dedicated videoconferencing equipment. The network (250) represents any number ofnetworks that convey coded video data among the terminal devices (210),(220), (230) and (240), including for example wireline (wired) and/orwireless communication networks. The communication network (250) mayexchange data in circuit-switched and/or packet-switched channels.Representative networks include telecommunications networks, local areanetworks, wide area networks and/or the Internet. For the purposes ofthe present discussion, the architecture and topology of the network(250) may be immaterial to the operation of the present disclosureunless explained herein below.

FIG. 3 illustrates, as an example for an application for the disclosedsubject matter, the placement of a video encoder and a video decoder ina streaming environment. The disclosed subject matter can be equallyapplicable to other video enabled applications, including, for example,video conferencing, digital TV, storing of compressed video on digitalmedia including CD, DVD, memory stick and the like, and so on.

A streaming system may include a capture subsystem (313), that caninclude a video source (301), for example a digital camera, creating forexample a stream of video pictures (302) that are uncompressed. In anexample, the stream of video pictures (302) includes samples that aretaken by the digital camera. The stream of video pictures (302),depicted as a bold line to emphasize a high data volume when compared toencoded video data (304) (or coded video bitstreams), can be processedby an electronic device (320) that includes a video encoder (303)coupled to the video source (301). The video encoder (303) can includehardware, software, or a combination thereof to enable or implementaspects of the disclosed subject matter as described in more detailbelow. The encoded video data (304) (or encoded video bitstream (304)),depicted as a thin line to emphasize the lower data volume when comparedto the stream of video pictures (302), can be stored on a streamingserver (305) for future use. One or more streaming client subsystems,such as client subsystems (306) and (308) in FIG. 3 can access thestreaming server (305) to retrieve copies (307) and (309) of the encodedvideo data (304). A client subsystem (306) can include a video decoder(310), for example, in an electronic device (330). The video decoder(310) decodes the incoming copy (307) of the encoded video data andcreates an outgoing stream of video pictures (311) that can be renderedon a display (312) (e.g., display screen) or other rendering device (notdepicted). In some streaming systems, the encoded video data (304),(307), and (309) (e.g., video bitstreams) can be encoded according tocertain video coding/compression standards. Examples of those standardsinclude ITU-T Recommendation H.265. In an example, a video codingstandard under development is informally known as Versatile Video Coding(VVC). The disclosed subject matter may be used in the context of VVC.

It is noted that the electronic devices (320) and (330) can includeother components (not shown). For example, the electronic device (320)can include a video decoder (not shown) and the electronic device (330)can include a video encoder (not shown) as well.

FIG. 4 shows a block diagram of a video decoder (410) according to anembodiment of the present disclosure. The video decoder (410) can beincluded in an electronic device (430). The electronic device (430) caninclude a receiver (431) (e.g., receiving circuitry). The video decoder(410) can be used in the place of the video decoder (310) in the FIG. 3example.

The receiver (431) may receive one or more coded video sequences to bedecoded by the video decoder (410); in the same or another embodiment,one coded video sequence at a time, where the decoding of each codedvideo sequence is independent from other coded video sequences. Thecoded video sequence may be received from a channel (401), which may bea hardware/software link to a storage device which stores the encodedvideo data. The receiver (431) may receive the encoded video data withother data, for example, coded audio data and/or ancillary data streams,that may be forwarded to their respective using entities (not depicted).The receiver (431) may separate the coded video sequence from the otherdata. To combat network jitter, a buffer memory (415) may be coupled inbetween the receiver (431) and an entropy decoder/parser (420) (“parser(420)” henceforth). In certain applications, the buffer memory (415) ispart of the video decoder (410). In others, it can be outside of thevideo decoder (410) (not depicted). In still others, there can be abuffer memory (not depicted) outside of the video decoder (410), forexample to combat network jitter, and in addition another buffer memory(415) inside the video decoder (410), for example to handle playouttiming. When the receiver (431) is receiving data from a store/forwarddevice of sufficient bandwidth and controllability, or from anisosynchronous network, the buffer memory (415) may not be needed, orcan be small. For use on best effort packet networks such as theInternet, the buffer memory (415) may be required, can be comparativelylarge and can be advantageously of adaptive size, and may at leastpartially be implemented in an operating system or similar elements (notdepicted) outside of the video decoder (410).

The video decoder (410) may include the parser (420) to reconstructsymbols (421) from the coded video sequence. Categories of those symbolsinclude information used to manage operation of the video decoder (410),and potentially information to control a rendering device such as arender device (412) (e.g., a display screen) that is not an integralpart of the electronic device (430) but can be coupled to the electronicdevice (430), as was shown in FIG. 4 . The control information for therendering device(s) may be in the form of Supplemental EnhancementInformation (SEI messages) or Video Usability Information (VUI)parameter set fragments (not depicted). The parser (420) mayparse/entropy-decode the coded video sequence that is received. Thecoding of the coded video sequence can be in accordance with a videocoding technology or standard, and can follow various principles,including variable length coding, Huffman coding, arithmetic coding withor without context sensitivity, and so forth. The parser (420) mayextract from the coded video sequence, a set of subgroup parameters forat least one of the subgroups of pixels in the video decoder, based uponat least one parameter corresponding to the group. Subgroups can includeGroups of Pictures (GOPs), pictures, tiles, slices, macroblocks, CodingUnits (CUs), blocks, Transform Units (TUs), Prediction Units (PUs) andso forth. The parser (420) may also extract from the coded videosequence information such as transform coefficients, quantizer parametervalues, motion vectors, and so forth.

The parser (420) may perform an entropy decoding/parsing operation onthe video sequence received from the buffer memory (415), so as tocreate symbols (421).

Reconstruction of the symbols (421) can involve multiple different unitsdepending on the type of the coded video picture or parts thereof (suchas: inter and intra picture, inter and intra block), and other factors.Which units are involved, and how, can be controlled by the subgroupcontrol information that was parsed from the coded video sequence by theparser (420). The flow of such subgroup control information between theparser (420) and the multiple units below is not depicted for clarity.

Beyond the functional blocks already mentioned, the video decoder (410)can be conceptually subdivided into a number of functional units asdescribed below. In a practical implementation operating undercommercial constraints, many of these units interact closely with eachother and can, at least partly, be integrated into each other. However,for the purpose of describing the disclosed subject matter, theconceptual subdivision into the functional units below is appropriate.

A first unit is the scaler/inverse transform unit (451). Thescaler/inverse transform unit (451) receives a quantized transformcoefficient as well as control information, including which transform touse, block size, quantization factor, quantization scaling matrices,etc. as symbol(s) (421) from the parser (420). The scaler/inversetransform unit (451) can output blocks comprising sample values, thatcan be input into aggregator (455).

In some cases, the output samples of the scaler/inverse transform (451)can pertain to an intra coded block; that is: a block that is not usingpredictive information from previously reconstructed pictures, but canuse predictive information from previously reconstructed parts of thecurrent picture. Such predictive information can be provided by an intrapicture prediction unit (452). In some cases, the intra pictureprediction unit (452) generates a block of the same size and shape ofthe block under reconstruction, using surrounding already reconstructedinformation fetched from the current picture buffer (458). The currentpicture buffer (458) buffers, for example, partly reconstructed currentpicture and/or fully reconstructed current picture. The aggregator(455), in some cases, adds, on a per sample basis, the predictioninformation the intra prediction unit (452) has generated to the outputsample information as provided by the scaler/inverse transform unit(451).

In other cases, the output samples of the scaler/inverse transform unit(451) can pertain to an inter coded, and potentially motion compensatedblock. In such a case, a motion compensation prediction unit (453) canaccess reference picture memory (457) to fetch samples used forprediction. After motion compensating the fetched samples in accordancewith the symbols (421) pertaining to the block, these samples can beadded by the aggregator (455) to the output of the scaler/inversetransform unit (451) (in this case called the residual samples orresidual signal) so as to generate output sample information. Theaddresses within the reference picture memory (457) from where themotion compensation prediction unit (453) fetches prediction samples canbe controlled by motion vectors, available to the motion compensationprediction unit (453) in the form of symbols (421) that can have, forexample X, Y, and reference picture components. Motion compensation alsocan include interpolation of sample values as fetched from the referencepicture memory (457) when sub-sample exact motion vectors are in use,motion vector prediction mechanisms, and so forth.

The output samples of the aggregator (455) can be subject to variousloop filtering techniques in the loop filter unit (456). Videocompression technologies can include in-loop filter technologies thatare controlled by parameters included in the coded video sequence (alsoreferred to as coded video bitstream) and made available to the loopfilter unit (456) as symbols (421) from the parser (420), but can alsobe responsive to meta-information obtained during the decoding ofprevious (in decoding order) parts of the coded picture or coded videosequence, as well as responsive to previously reconstructed andloop-filtered sample values.

The output of the loop filter unit (456) can be a sample stream that canbe output to the render device (412) as well as stored in the referencepicture memory (457) for use in future inter-picture prediction.

Certain coded pictures, once fully reconstructed, can be used asreference pictures for future prediction. For example, once a codedpicture corresponding to a current picture is fully reconstructed andthe coded picture has been identified as a reference picture (by, forexample, the parser (420)), the current picture buffer (458) can becomea part of the reference picture memory (457), and a fresh currentpicture buffer can be reallocated before commencing the reconstructionof the following coded picture.

The video decoder (410) may perform decoding operations according to apredetermined video compression technology in a standard, such as ITU-TRec. H.265. The coded video sequence may conform to a syntax specifiedby the video compression technology or standard being used, in the sensethat the coded video sequence adheres to both the syntax of the videocompression technology or standard and the profiles as documented in thevideo compression technology or standard. Specifically, a profile canselect certain tools as the only tools available for use under thatprofile from all the tools available in the video compression technologyor standard. Also necessary for compliance can be that the complexity ofthe coded video sequence is within bounds as defined by the level of thevideo compression technology or standard. In some cases, levels restrictthe maximum picture size, maximum frame rate, maximum reconstructionsample rate (measured in, for example megasamples per second), maximumreference picture size, and so on. Limits set by levels can, in somecases, be further restricted through Hypothetical Reference Decoder(HRD) specifications and metadata for HRD buffer management signaled inthe coded video sequence.

In an embodiment, the receiver (431) may receive additional (redundant)data with the encoded video. The additional data may be included as partof the coded video sequence(s). The additional data may be used by thevideo decoder (410) to properly decode the data and/or to moreaccurately reconstruct the original video data. Additional data can bein the form of, for example, temporal, spatial, or signal noise ratio(SNR) enhancement layers, redundant slices, redundant pictures, forwarderror correction codes, and so on.

FIG. 5 shows a block diagram of a video encoder (503) according to anembodiment of the present disclosure. The video encoder (503) isincluded in an electronic device (520). The electronic device (520)includes a transmitter (540) (e.g., transmitting circuitry). The videoencoder (503) can be used in the place of the video encoder (303) in theFIG. 3 example.

The video encoder (503) may receive video samples from a video source(501) (that is not part of the electronic device (520) in the FIG. 5example) that may capture video image(s) to be coded by the videoencoder (503). In another example, the video source (501) is a part ofthe electronic device (520).

The video source (501) may provide the source video sequence to be codedby the video encoder (503) in the form of a digital video sample streamthat can be of any suitable bit depth (for example: 8 bit, 10 bit, 12bit, . . . ), any colorspace (for example, BT.601 Y CrCB, RGB, . . . ),and any suitable sampling structure (for example Y CrCb 4:2:0, Y CrCb4:4:4). In a media serving system, the video source (501) may be astorage device storing previously prepared video. In a videoconferencingsystem, the video source (501) may be a camera that captures local imageinformation as a video sequence. Video data may be provided as aplurality of individual pictures that impart motion when viewed insequence. The pictures themselves may be organized as a spatial array ofpixels, wherein each pixel can comprise one or more samples depending onthe sampling structure, color space, etc. in use. A person skilled inthe art can readily understand the relationship between pixels andsamples. The description below focuses on samples.

According to an embodiment, the video encoder (503) may code andcompress the pictures of the source video sequence into a coded videosequence (543) in real time or under any other time constraints asrequired by the application. Enforcing appropriate coding speed is onefunction of a controller (550). In some embodiments, the controller(550) controls other functional units as described below and isfunctionally coupled to the other functional units. The coupling is notdepicted for clarity. Parameters set by the controller (550) can includerate control related parameters (picture skip, quantizer, lambda valueof rate-distortion optimization techniques, . . . ), picture size, groupof pictures (GOP) layout, maximum motion vector search range, and soforth. The controller (550) can be configured to have other suitablefunctions that pertain to the video encoder (503) optimized for acertain system design.

In some embodiments, the video encoder (503) is configured to operate ina coding loop. As an oversimplified description, in an example, thecoding loop can include a source coder (530) (e.g., responsible forcreating symbols, such as a symbol stream, based on an input picture tobe coded, and a reference picture(s)), and a (local) decoder (533)embedded in the video encoder (503). The decoder (533) reconstructs thesymbols to create the sample data in a similar manner as a (remote)decoder also would create (as any compression between symbols and codedvideo bitstream is lossless in the video compression technologiesconsidered in the disclosed subject matter). The reconstructed samplestream (sample data) is input to the reference picture memory (534). Asthe decoding of a symbol stream leads to bit-exact results independentof decoder location (local or remote), the content in the referencepicture memory (534) is also bit exact between the local encoder andremote encoder. In other words, the prediction part of an encoder “sees”as reference picture samples exactly the same sample values as a decoderwould “see” when using prediction during decoding. This fundamentalprinciple of reference picture synchronicity (and resulting drift, ifsynchronicity cannot be maintained, for example because of channelerrors) is used in some related arts as well.

The operation of the “local” decoder (533) can be the same as of a“remote” decoder, such as the video decoder (410), which has alreadybeen described in detail above in conjunction with FIG. 4 . Brieflyreferring also to FIG. 4 , however, as symbols are available andencoding/decoding of symbols to a coded video sequence by an entropycoder (545) and the parser (420) can be lossless, the entropy decodingparts of the video decoder (410), including the buffer memory (415), andparser (420) may not be fully implemented in the local decoder (533).

An observation that can be made at this point is that any decodertechnology except the parsing/entropy decoding that is present in adecoder also necessarily needs to be present, in substantially identicalfunctional form, in a corresponding encoder. For this reason, thedisclosed subject matter focuses on decoder operation. The descriptionof encoder technologies can be abbreviated as they are the inverse ofthe comprehensively described decoder technologies. Only in certainareas a more detail description is required and provided below.

During operation, in some examples, the source coder (530) may performmotion compensated predictive coding, which codes an input picturepredictively with reference to one or more previously-coded picture fromthe video sequence that were designated as “reference pictures”. In thismanner, the coding engine (532) codes differences between pixel blocksof an input picture and pixel blocks of reference picture(s) that may beselected as prediction reference(s) to the input picture.

The local video decoder (533) may decode coded video data of picturesthat may be designated as reference pictures, based on symbols createdby the source coder (530). Operations of the coding engine (532) mayadvantageously be lossy processes. When the coded video data may bedecoded at a video decoder (not shown in FIG. 5 ), the reconstructedvideo sequence typically may be a replica of the source video sequencewith some errors. The local video decoder (533) replicates decodingprocesses that may be performed by the video decoder on referencepictures and may cause reconstructed reference pictures to be stored inthe reference picture cache (534). In this manner, the video encoder(503) may store copies of reconstructed reference pictures locally thathave common content as the reconstructed reference pictures that will beobtained by a far-end video decoder (absent transmission errors).

The predictor (535) may perform prediction searches for the codingengine (532). That is, for a new picture to be coded, the predictor(535) may search the reference picture memory (534) for sample data (ascandidate reference pixel blocks) or certain metadata such as referencepicture motion vectors, block shapes, and so on, that may serve as anappropriate prediction reference for the new pictures. The predictor(535) may operate on a sample block-by-pixel block basis to findappropriate prediction references. In some cases, as determined bysearch results obtained by the predictor (535), an input picture mayhave prediction references drawn from multiple reference pictures storedin the reference picture memory (534).

The controller (550) may manage coding operations of the source coder(530), including, for example, setting of parameters and subgroupparameters used for encoding the video data.

Output of all aforementioned functional units may be subjected toentropy coding in the entropy coder (545). The entropy coder (545)translates the symbols as generated by the various functional units intoa coded video sequence, by lossless compressing the symbols according totechnologies such as Huffman coding, variable length coding, arithmeticcoding, and so forth.

The transmitter (540) may buffer the coded video sequence(s) as createdby the entropy coder (545) to prepare for transmission via acommunication channel (560), which may be a hardware/software link to astorage device which would store the encoded video data. The transmitter(540) may merge coded video data from the video coder (503) with otherdata to be transmitted, for example, coded audio data and/or ancillarydata streams (sources not shown).

The controller (550) may manage operation of the video encoder (503).During coding, the controller (550) may assign to each coded picture acertain coded picture type, which may affect the coding techniques thatmay be applied to the respective picture. For example, pictures oftenmay be assigned as one of the following picture types:

An Intra Picture (I picture) may be one that may be coded and decodedwithout using any other picture in the sequence as a source ofprediction. Some video codecs allow for different types of intrapictures, including, for example Independent Decoder Refresh (“IDR”)Pictures. A person skilled in the art is aware of those variants of Ipictures and their respective applications and features.

A predictive picture (P picture) may be one that may be coded anddecoded using intra prediction or inter prediction using at most onemotion vector and reference index to predict the sample values of eachblock.

A bi-directionally predictive picture (B Picture) may be one that may becoded and decoded using intra prediction or inter prediction using atmost two motion vectors and reference indices to predict the samplevalues of each block. Similarly, multiple-predictive pictures can usemore than two reference pictures and associated metadata for thereconstruction of a single block.

Source pictures commonly may be subdivided spatially into a plurality ofsample blocks (for example, blocks of 4×4, 8×8, 4×8, or 16×16 sampleseach) and coded on a block-by-block basis. Blocks may be codedpredictively with reference to other (already coded) blocks asdetermined by the coding assignment applied to the blocks' respectivepictures. For example, blocks of I pictures may be codednon-predictively or they may be coded predictively with reference toalready coded blocks of the same picture (spatial prediction or intraprediction). Pixel blocks of P pictures may be coded predictively, viaspatial prediction or via temporal prediction with reference to onepreviously coded reference picture. Blocks of B pictures may be codedpredictively, via spatial prediction or via temporal prediction withreference to one or two previously coded reference pictures.

The video encoder (503) may perform coding operations according to apredetermined video coding technology or standard, such as ITU-T Rec.H.265. In its operation, the video encoder (503) may perform variouscompression operations, including predictive coding operations thatexploit temporal and spatial redundancies in the input video sequence.The coded video data, therefore, may conform to a syntax specified bythe video coding technology or standard being used.

In an embodiment, the transmitter (540) may transmit additional datawith the encoded video. The source coder (530) may include such data aspart of the coded video sequence. Additional data may comprisetemporal/spatial/SNR enhancement layers, other forms of redundant datasuch as redundant pictures and slices, SEI messages, VUI parameter setfragments, and so on.

A video may be captured as a plurality of source pictures (videopictures) in a temporal sequence. Intra-picture prediction (oftenabbreviated to intra prediction) makes use of spatial correlation in agiven picture, and inter-picture prediction makes uses of the (temporalor other) correlation between the pictures. In an example, a specificpicture under encoding/decoding, which is referred to as a currentpicture, is partitioned into blocks. When a block in the current pictureis similar to a reference block in a previously coded and still bufferedreference picture in the video, the block in the current picture can becoded by a vector that is referred to as a motion vector. The motionvector points to the reference block in the reference picture, and canhave a third dimension identifying the reference picture, in casemultiple reference pictures are in use.

In some embodiments, a bi-prediction technique can be used in theinter-picture prediction. According to the bi-prediction technique, tworeference pictures, such as a first reference picture and a secondreference picture that are both prior in decoding order to the currentpicture in the video (but may be in the past and future, respectively,in display order) are used. A block in the current picture can be codedby a first motion vector that points to a first reference block in thefirst reference picture, and a second motion vector that points to asecond reference block in the second reference picture. The block can bepredicted by a combination of the first reference block and the secondreference block.

Further, a merge mode technique can be used in the inter-pictureprediction to improve coding efficiency.

According to some embodiments of the disclosure, predictions, such asinter-picture predictions and intra-picture predictions are performed inthe unit of blocks. For example, according to the HEVC standard, apicture in a sequence of video pictures is partitioned into coding treeunits (CTU) for compression, the CTUs in a picture have the same size,such as 64×64 pixels, 32×32 pixels, or 16×16 pixels. In general, a CTUincludes three coding tree blocks (CTBs), which are one luma CTB and twochroma CTBs. Each CTU can be recursively quadtree split into one ormultiple coding units (CUs). For example, a CTU of 64×64 pixels can besplit into one CU of 64×64 pixels, or 4 CUs of 32×32 pixels, or 16 CUsof 16×16 pixels. In an example, each CU is analyzed to determine aprediction type for the CU, such as an inter prediction type or an intraprediction type. The CU is split into one or more prediction units (PUs)depending on the temporal and/or spatial predictability. Generally, eachPU includes a luma prediction block (PB), and two chroma PBs. In anembodiment, a prediction operation in coding (encoding/decoding) isperformed in the unit of a prediction block. Using a luma predictionblock as an example of a prediction block, the prediction block includesa matrix of values (e.g., luma values) for pixels, such as 8×8 pixels,16×16 pixels, 8×16 pixels, 16×8 pixels, and the like.

FIG. 6 shows a diagram of a video encoder (603) according to anotherembodiment of the disclosure. The video encoder (603) is configured toreceive a processing block (e.g., a prediction block) of sample valueswithin a current video picture in a sequence of video pictures, andencode the processing block into a coded picture that is part of a codedvideo sequence. In an example, the video encoder (603) is used in theplace of the video encoder (303) in the FIG. 3 example.

In an HEVC example, the video encoder (603) receives a matrix of samplevalues for a processing block, such as a prediction block of 8×8samples, and the like. The video encoder (603) determines whether theprocessing block is best coded using intra mode, inter mode, orbi-prediction mode using, for example, rate-distortion optimization.When the processing block is to be coded in intra mode, the videoencoder (603) may use an intra prediction technique to encode theprocessing block into the coded picture; and when the processing blockis to be coded in inter mode or bi-prediction mode, the video encoder(603) may use an inter prediction or bi-prediction technique,respectively, to encode the processing block into the coded picture. Incertain video coding technologies, merge mode can be an inter pictureprediction submode where the motion vector is derived from one or moremotion vector predictors without the benefit of a coded motion vectorcomponent outside the predictors. In certain other video codingtechnologies, a motion vector component applicable to the subject blockmay be present. In an example, the video encoder (603) includes othercomponents, such as a mode decision module (not shown) to determine themode of the processing blocks.

In the FIG. 6 example, the video encoder (603) includes the interencoder (630), an intra encoder (622), a residue calculator (623), aswitch (626), a residue encoder (624), a general controller (621), andan entropy encoder (625) coupled together as shown in FIG. 6 .

The inter encoder (630) is configured to receive the samples of thecurrent block (e.g., a processing block), compare the block to one ormore reference blocks in reference pictures (e.g., blocks in previouspictures and later pictures), generate inter prediction information(e.g., description of redundant information according to inter encodingtechnique, motion vectors, merge mode information), and calculate interprediction results (e.g., predicted block) based on the inter predictioninformation using any suitable technique. In some examples, thereference pictures are decoded reference pictures that are decoded basedon the encoded video information.

The intra encoder (622) is configured to receive the samples of thecurrent block (e.g., a processing block), in some cases compare theblock to blocks already coded in the same picture, generate quantizedcoefficients after transform, and in some cases also intra predictioninformation (e.g., an intra prediction direction information accordingto one or more intra encoding techniques). In an example, the intraencoder (622) also calculates intra prediction results (e.g., predictedblock) based on the intra prediction information and reference blocks inthe same picture.

The general controller (621) is configured to determine general controldata and control other components of the video encoder (603) based onthe general control data. In an example, the general controller (621)determines the mode of the block, and provides a control signal to theswitch (626) based on the mode. For example, when the mode is the intramode, the general controller (621) controls the switch (626) to selectthe intra mode result for use by the residue calculator (623), andcontrols the entropy encoder (625) to select the intra predictioninformation and include the intra prediction information in thebitstream; and when the mode is the inter mode, the general controller(621) controls the switch (626) to select the inter prediction resultfor use by the residue calculator (623), and controls the entropyencoder (625) to select the inter prediction information and include theinter prediction information in the bitstream.

The residue calculator (623) is configured to calculate a difference(residue data) between the received block and prediction resultsselected from the intra encoder (622) or the inter encoder (630). Theresidue encoder (624) is configured to operate based on the residue datato encode the residue data to generate the transform coefficients. In anexample, the residue encoder (624) is configured to convert the residuedata from a spatial domain to a frequency domain, and generate thetransform coefficients. The transform coefficients are then subject toquantization processing to obtain quantized transform coefficients. Invarious embodiments, the video encoder (603) also includes a residuedecoder (628). The residue decoder (628) is configured to performinverse-transform, and generate the decoded residue data. The decodedresidue data can be suitably used by the intra encoder (622) and theinter encoder (630). For example, the inter encoder (630) can generatedecoded blocks based on the decoded residue data and inter predictioninformation, and the intra encoder (622) can generate decoded blocksbased on the decoded residue data and the intra prediction information.The decoded blocks are suitably processed to generate decoded picturesand the decoded pictures can be buffered in a memory circuit (not shown)and used as reference pictures in some examples.

The entropy encoder (625) is configured to format the bitstream toinclude the encoded block. The entropy encoder (625) is configured toinclude various information according to a suitable standard, such asthe HEVC standard. In an example, the entropy encoder (625) isconfigured to include the general control data, the selected predictioninformation (e.g., intra prediction information or inter predictioninformation), the residue information, and other suitable information inthe bitstream. Note that, according to the disclosed subject matter,when coding a block in the merge submode of either inter mode orbi-prediction mode, there is no residue information.

FIG. 7 shows a diagram of a video decoder (710) according to anotherembodiment of the disclosure. The video decoder (710) is configured toreceive coded pictures that are part of a coded video sequence, anddecode the coded pictures to generate reconstructed pictures. In anexample, the video decoder (710) is used in the place of the videodecoder (310) in the FIG. 3 example.

In the FIG. 7 example, the video decoder (710) includes an entropydecoder (771), an inter decoder (780), a residue decoder (773), areconstruction module (774), and an intra decoder (772) coupled togetheras shown in FIG. 7 .

The entropy decoder (771) can be configured to reconstruct, from thecoded picture, certain symbols that represent the syntax elements ofwhich the coded picture is made up. Such symbols can include, forexample, the mode in which a block is coded (such as, for example, intramode, inter mode, bi-predicted mode, the latter two in merge submode oranother submode), prediction information (such as, for example, intraprediction information or inter prediction information) that canidentify certain sample or metadata that is used for prediction by theintra decoder (772) or the inter decoder (780), respectively, residualinformation in the form of, for example, quantized transformcoefficients, and the like. In an example, when the prediction mode isinter or bi-predicted mode, the inter prediction information is providedto the inter decoder (780); and when the prediction type is the intraprediction type, the intra prediction information is provided to theintra decoder (772). The residual information can be subject to inversequantization and is provided to the residue decoder (773).

The inter decoder (780) is configured to receive the inter predictioninformation, and generate inter prediction results based on the interprediction information.

The intra decoder (772) is configured to receive the intra predictioninformation, and generate prediction results based on the intraprediction information.

The residue decoder (773) is configured to perform inverse quantizationto extract de-quantized transform coefficients, and process thede-quantized transform coefficients to convert the residual from thefrequency domain to the spatial domain. The residue decoder (773) mayalso require certain control information (to include the QuantizerParameter (QP)), and that information may be provided by the entropydecoder (771) (data path not depicted as this may be low volume controlinformation only).

The reconstruction module (774) is configured to combine, in the spatialdomain, the residual as output by the residue decoder (773) and theprediction results (as output by the inter or intra prediction modulesas the case may be) to form a reconstructed block, that may be part ofthe reconstructed picture, which in turn may be part of thereconstructed video. It is noted that other suitable operations, such asa deblocking operation and the like, can be performed to improve thevisual quality.

It is noted that the video encoders (303), (503), and (603), and thevideo decoders (310), (410), and (710) can be implemented using anysuitable technique. In an embodiment, the video encoders (303), (503),and (603), and the video decoders (310), (410), and (710) can beimplemented using one or more integrated circuits. In anotherembodiment, the video encoders (303), (503), and (503), and the videodecoders (310), (410), and (710) can be implemented using one or moreprocessors that execute software instructions.

In some embodiments, a motion vector may have an integer-pixel precisionsuch that the motion vector points to a pixel position for identifying areference block. In some embodiments, a motion vector may have afractional-pixel precision such that the motion vector points to afractional pixel position for identifying a reference block. Tocalculate pixel values at fractional pixel positions, an interpolationfilters may be used, which may require additional pixels outside theintended reference block for interpolation operations.

For example, in HEVC, to calculate pixel values at fractional pixelpositions, 8-tap and 4-tap separable interpolation filters are used forluma and chroma components, respectively. For an M×N luma blockinterpolation, (M+7)×(N+7) luma samples need to be loaded from areference picture according to the integer-pixel parts of the motionvectors. Accordingly, in HEVC, for a 4×4 luma uni-directional interprediction, the decoder may need to load up to (4+7)×(4+7)=121 lumasamples for performing the interpolation process. The per-pixel memorybandwidth requirement for this example is about 7.6 sample/pixel (121samples for a 16-pixel block). Also, for a 4×4 luma bi-directional interprediction, the requirement may double to become 15.125 sample/pixel.

In some embodiments, limiting the size of a block that is coded usinginter prediction reduces the memory bandwidth requirement. For example,if the minimal block size of a block coded using the bi-directionalinter prediction is limited to 8×8 pixels, the per-pixel memorybandwidth requirement can be reduced to 7.0 sample/pixel (450 samplesfor a 64-pixel block). Therefore, in some embodiments for interprediction blocks smaller than 8×8, only uni-directional interprediction is allowed.

FIG. 8 is a schematic illustration of spatial neighboring blocks thatcan be used to determine motion information for a current block (801)using an affine motion compensation method in accordance with anembodiment. FIG. 8 shows a current block (801) and its spatialneighboring blocks denoted A0, A1, A2, B0, B1, B2, and B3 (802, 803,807, 804, 805, 806, and 808, respectively). In some examples, spatialneighboring blocks A0, A1, A2, B0, B1, B2, and B3 and the current block(801) belong to a same picture.

Affine motion compensation, by describing a 6-parameter (or a simplified4-parameter) model for a coding block, such as the current block (801),can efficiently predict the motion information for all samples withinthe current block with respect to a particular reference picture in aparticular prediction direction. In some embodiments, in an affine codedor described coding block, different part of the samples can havedifferent motion vectors with respect to the particular reference. Thebasic unit to have a motion vector in an affine coded or described blockis referred to as a sub-block. The size of a sub-block can be as smallas 1 sample only; and can be as large as the size of current block.

In some examples, an affine model uses 6 parameters to describe themotion information of an affine coded block, which can be represented bythree motion vectors (also referred to as three control point motionvectors) at three different locations of the block (e.g., control pointsCP0, CP1, and CP2 at top-left, top-right, and bottom-left corners inFIG. 8 ). In another example, a simplified affine model uses fourparameters to describe the motion information of an affine coded block,which can be represented by two motion vectors (also referred to as twocontrol point motion vectors) at two different locations of the block(e.g., control points CP0 and CP1 at top-left and top-right corners inFIG. 8 ).

In some embodiments, the motion information for the control points CP0,CP1, and CP2 can be derived from motion information of the spatialneighboring blocks A0, A1, A2, B0, B1, B2, and B3. For example, thecontrol points CP0 can be derived based on checking the motioninformation of the spatial neighboring blocks B2, A2, and B3; thecontrol points CP1 can be derived based on checking the motioninformation of the spatial neighboring blocks B0 and B1; and the controlpoints CP2 can be derived based on checking the motion information ofthe spatial neighboring blocks A0 and A1.

When an affine mode is determined, the motion vector (with respect tothe particular reference picture) can be derived using such a model. Insome embodiments, in order to reduce implementation complexity, theaffine motion compensation is performed on a sub-block basis, instead ofon a sample basis. Accordingly, in such embodiments, each sub-blockwithin the current block (801) has a corresponding motion vector withrespect to the particular reference that is applicable to all samples inthe respective sub-block. In some examples, the representative locationof each sub-block can be signaled or predetermined according to a videocoding standard. In some examples, a location of a sub-block can berepresented by a top-left or a center point of the sub-block. In anexample using VVC, a sub-block may have a size of 4×4 samples.

FIG. 9 is a schematic illustration of temporal reference blocks that canbe used to determine motion information (including motion vectors andreference indices) for a current block (911) using a Sub-block temporalMV prediction (SbTMVP) method (or sometimes also referred to as analternative temporal motion vector prediction (ATMVP) method) inaccordance with one embodiment. In some examples, the SbTMVP method canbe implemented by modifying the temporal motion vector prediction (TMVP)method by fetching multiple sets of motion information from blockssmaller than the current block (911).

FIG. 9 shows a current block (911) in a current picture (910) and areference block (961) is in a reference picture (960). The referenceblock (961) can be identified based on a motion shift (or displacement)between the current block (911) and the reference block (961) indicatedby a temporal vector (922). In some embodiments, the reference block(961) corresponds to a coding block in the reference picture (960). Insome embodiments, the reference block (961) is just a counterpart regionof the current block (911) in the reference picture (960) and does notcorrespond to any coding block in the reference picture (960).

Moreover, the current block (911) includes a plurality of sub-blocks(e.g., sub-blocks 911 a, 911 b, 911 c, and 911 d), and the referenceblock (961) includes a plurality of sub-blocks (e.g., sub-blocks 961 a,961 b, 961 c, and 961 d) that corresponds to the counterpart regions ofthe sub-blocks (911 a, 911 b, 911 c, and 911 d) of the current block(911). The sub-blocks (911 a, 911 b, 911 c, and 911 d) includerespective motion information (MVa, MVb, MVc, and MVd), and thesub-blocks (961 a, 961 b, 961 c, and 961 d) include respective referencemotion information (MRa, MRb, MRc, and MRd). In some embodiments, eachof the sub-blocks (911 a, 911 b, 911 c, and 911 d) has a size of 4×4samples.

According to some embodiments that use SbTMVP methods, the motioninformation (MVa, MVb, MVc, and MVd) of the sub-blocks (911 a, 911 b,911 c, and 911 d) within the current block (911) can be determined byidentifying the corresponding reference block (961) in the referencepicture (960) with the temporal vector (922), splitting the currentblock (911) into sub-blocks (911 a, 911 b, 911 c, and 911 d) and thereference block (961) into sub-blocks (961 a, 961 b, 961 c, and 961 d),obtaining the motion information (MRa, MRb, MRc, and MRd) of thesub-blocks (961 a, 961 b, 961 c, and 961 d), and determining the motioninformation (MVa, MVb, MVc, and MVd) of the sub-blocks (911 a, 911 b,911 c, and 911 d) according to the motion information (MRa, MRb, MRc,and MRd) of the sub-blocks (961 a, 961 b, 961 c, and 961 d),respectively.

In some embodiments, the reference picture (960) and the correspondingreference block (961) can be determined by the motion information of thespatial neighboring blocks of the current block (910). In someembodiments, to avoid a repetitive scanning process for scanning thespatial neighboring blocks, a first merge candidate in a merge candidatelist of the current block (911) can be used. The first available motionvector as well as a reference index associated with the first availablemotion vector are set to be the temporal vector (922) and the index tothe reference picture (960). Accordingly, comparing the SbTMVP method tothe TMVP method, the corresponding reference block (961) according tothe SbTMVP method may be more accurately identified, while thecorresponding reference block (sometimes called the collocated block)according to the TMVP method is set to a block corresponding to abottom-right corner or a center position with respect to the currentblock.

Moreover, for each sub-block (911 a, 911 b, 911 c, or 911 d) of thecurrent block (911), the motion information (MRa, MRb, MRc, or MRd) ofthe corresponding sub-block (961 a, 961 b, 961 c, or 961 d) in thereference picture (960) can be used to derive the corresponding motioninformation (MVa, MVb, MVc, or MVd) of the sub-block (911 a, 911 b, 911c, or 911 d). In some embodiments, the motion information (MRa, MRb,MRc, and MRd) of the sub-blocks (961 a, 961 b, 961 c, and 961 d)corresponds to the motion information of the smallest motion grid in thereference picture (960) that covers the center sample of the respectivesub-blocks (911 a, 911 b, 911 c, and 911 d). After the motioninformation (MRa, MRb, MRc, or MRd) of a sub-block (961 a, 961 b, 961 c,or 961 d) in the reference picture (960) is obtained, the motioninformation of a corresponding sub-block (911 a, 911 b, 911 c, or 911 d)of the current block (911) can be derived by converting the motioninformation (MRa, MRb, MRc, or MRd) in a manner similar to the TMVPmethod, including motion scaling and other suitable conversion process.

In some examples, when a low-delay condition (i.e., the POCs of allreference pictures of the current picture are smaller than the POC ofthe current picture) is met, a motion vector corresponding to onereference picture list (e.g., one of list 0 and list 1) can be used topredict motion vectors corresponding to another reference picture list(e.g., the other one of list 0 and list 1) for the sub-blocks of thecurrent picture.

FIGS. 10A and 10B are schematics illustration of spatial neighboringblocks and a temporal neighboring block that can be used to determinemotion information for a current block (1010) using a planar motionvector prediction method in accordance with an embodiment. In someembodiments, a motion vector obtained according to the planar motionvector prediction method can be used as a special merge candidate on asub-block basis. The planar motion vector prediction method can be usedto generate a smooth and fine granularity motion field.

As shown in FIGS. 10A and 10B, the current block (1010) has a size ofwidth W and height H and includes 8×8 sub-blocks as an example, whereeach sub-block may have a size of 4×4 samples. In other embodiments, thecurrent block (1010) can include a number of sub-blocks other than 8×8sub-blocks, and each sub-block may have a size different from 4×4samples. In FIGS. 10A and 10B, blocks 1020[1]˜1020[8] are spatialneighboring blocks adjacent to an upper edge of the current block(1010); blocks 1030[1]˜1030[8] are spatial neighboring blocks adjacentto a left edge of the current block (1010); block 1022 is a spatialneighboring blocks adjacent to a top-left corner of the current block(1010); block 1024 is a spatial neighboring blocks adjacent to atop-right corner of the current block (1010); and block 1032 is aspatial neighboring blocks adjacent to a bottom-left corner of thecurrent block (1010). Moreover, block (1040) is a temporal neighboringblocks that is located at a position outside a region corresponding tothe current block (1010) and adjacent to a bottom-right corner of theregion.

As shown in FIG. 10A, in one example, a top-left corner of the currentblock (1010) has a position (0, 0) and a sub-block (1060) has a position(x, y). The left neighboring block (1030[4]), the sub-block (1060), anda right block (1052) are in a same row ‘y,’ where the right block (1052)has a position (W, y), where W corresponds to the width of block (1010).The motion information of the right block (1052) can be determined byinterpolation based on the motion information of the neighboring block(1024) and the motion information of the temporal neighboring block(1040).

A horizontal motion vector prediction P_(h)(x, y) for the sub-block(1060) at the position (x, y) in the current block (1010) can becalculated via a linear interpolation on a 4×4 block basis according tothe following equation:

P _(h)(x,y)=(W−1−x)×L(−1,y)+(x+1)×R(W,y),

where L(−1, y) and R(W, y) represent the motion vectors of the leftneighboring block (1030[4]) and the block (1052), respectively, where Wcorresponds to the width of block (1010).

In addition, as shown in FIG. 10B, in one example, top neighboring block(1020[3]), the sub-block (1060), and a bottom block (1054) are in a samecolumn ‘x,’ where the block (1054) has a position (x, H), where H is theheight of block (1010). The motion information of the bottom block(1054) can be determined by interpolation based on the motioninformation of the neighboring block (1032) and the motion informationof the temporal neighboring block (1040).

A vertical motion vector prediction P_(v)(x, y) for the sub-block (1060)at the position (x, y) in the current block (1010) can be calculated viaa linear interpolation on a 4×4 block basis according to the followingequation:

P _(v)(x,y)=(H−1−y)×A(x,−1)+(y+1)×B(x,H),

where A(x, −1) and B(x, H) represent the motion vectors of the block(1020[3]) and the block (1054), respectively, where H corresponds to theheight of block (1010).

Referring to FIGS. 10A and 10B, a motion vector or a motion vectorcandidate can determined according to the planar motion vectorprediction can be achieved by averaging the horizontal predictionP_(h)(x, y) and the vertical prediction P_(v)(x, y) to determine aplanar motion vector P(x, y) according to the following equation:

P(x,y)=(H×P _(h)(x,y)+W×P _(v)(x,y)+H×W)/(2×H×W).

In some embodiments, the motion vector of the right neighboring block(1052) can be determined according to the following equation:

R(W,y)=((H−y−1)×AR+(y+1)×BR)/H,

where AR represent the motion vector of the block (1024), and BRrepresents the motion vector of the block (1054).

In some embodiments, the motion vector of the bottom neighboring block(1054) can be determined according to the following equation:

B(x,H)=((W−x−1)×BL+(x+1)×BR)/W,

where BL represent the motion vector of the block (1032), and BRrepresents the motion vector of the block (1054).

In some embodiments, for an inter prediction mode that uses sub-blocks,the smaller the sub-block size, the greater the memory bandwidthrequirement per pixel is required, and such memory bandwidthrequirements can be doubled for bi-directional inter prediction.However, the coding efficiency may decrease when the sub-block size isset to be a larger size. In some embodiments, the motion vectors of agroup of sub-blocks (or a group of blocks) can be adjusted within apredetermined range, such that the reference samples for the group ofsub-blocks (or the group of blocks) collectively can be processed as ifit is for a consolidated block that covers the group of sub-blocks (orthe group of blocks). Accordingly, in some embodiments, the codingscheme can benefit from both the precision of a smaller sub-block (orblock) size and the reduced memory bandwidth requirement per pixel of agreater sub-block (or block) size. In some embodiments, the motionvector adjustment as described in this disclosure can improve the memorybandwidth requirement per pixel for a group of sub-blocks (or a group ofblocks) of a size of 4×4 samples that are used for bi-directionalinter-prediction.

In some embodiments, the motion vectors of a group of sub-blocks (e.g.,sub-blocks of a coding unit, a coding block, or a prediction block) canbe adjusted according to one or more of various motion vector adjustmentschemes described herein. For the purpose of describing various motionvector adjustment schemes, a group of sub-blocks of a W×H inter block(having a size of width W and height H) is used as an example. In someembodiments, the motion vector adjustment schemes can also be applicableto a group of blocks, where the term of block may correspond to a codingunit, a coding block, or a prediction block.

In some embodiments, according to a first motion vector adjustmentscheme, for a W×H inter block which is coded in a sub-block mode, suchas affine, SbTMVP, planar MV prediction, etc., the motion vectors of thesub-blocks (i.e., sub-block MVs) inside a M×N block area (M<=W, N<=H)and pointing to a particular reference picture in a particular referencelist can be checked and limited to a range such that the maximumabsolute difference between the integer-pixel parts of the sub-block MVsalong a particular coordinate direction is equal to or less than atarget difference. For example, the motion vectors of sub-blocks in theM×N block area after the motion vector adjustment process, or alsoreferred to as target motion vectors, can be limited to a range alongthe x coordinate direction such that a difference of integer-pixel partsthereof along the x coordinate direction is equal to or less than atarget difference for the x coordinate direction. Additionally oralternatively, in some examples, the target motion vectors can belimited to a range along the y coordinate direction such that adifference of integer-pixel parts thereof along the y coordinatedirection is equal to or less than a target difference for the ycoordinate direction.

By adjusting the motion vectors as described herein, the referencesamples to be loaded for the interpolation of all sub-blocks inside M×Nblock area block can be confined within an area defined by M, N, theinterpolation tap (or interpolation taps if different taps are used fordifferent coordinate directions), and the target difference (or targetdifferences if different target differences are used for differentcoordinate directions). Accordingly, the maximum number of the totalsamples to be loaded for the group of sub-blocks can be reduced or atleast more predictable for band-width management purposes.

The target difference or target differences, M, N, and/or sub-block sizemay be predefined, or signaled in a coded video bitstream, such as in asequence parameter set (SPS) header, a picture parameter set (PPS)header, a slice header, a tile header, video usage information (VUI), ora supplemental enhancement information (SEI) message of the coded videobitstream.

In one example, M is set to 8 and N is set to 8, the sub-block size is4×4 samples, and the target difference is set to 1 pixel for both the xcoordinate direction and the y coordinate direction. Therefore, thereare four 4×4 sub-blocks in an 8×8 block area. The maximum absolutedifference of integer-pixel part in the x direction and in the ydirection among all the four motion vectors of the four sub-blocks canbe limited to not exceeding a target difference, which can be 1 integerpixel for each prediction list (e.g., List0 or Lsit1).

In some embodiments, the motion vectors of sub-blocks in an M×N blockarea, or also referred to as base motion vectors that are determinedprior to a motion vector adjustment process, can be limited to a lowerbound MVminx and an upper bound MVmaxx for components along the xcoordinate direction and a lower bound MVminy and an upper bound MVmaxyfor components along the y coordinate direction. The correspondingMVminx, MVmaxx, MVminy, and MVmaxy values can be determined for each M×Nblock area. In some examples, a motion vector (MVxi, MVyi) of asub-block i inside an M×N block area can be clipped (or adjusted bytruncation) according to max(MVminx, min(MVmaxx, MVxi)) along the xcoordinate direction and max(MVminy, min(MVmaxy, MVyi)) along the ycoordinate direction, where MVxi is an x coordinate direction component,MVyi is a y coordinate direction component, min(a, b) represents a lowervalue between a and b, and max(a, b) represents a greater value betweena and b. Also, the absolute difference of the integer-pixel part ofMVmaxx and the integer-pixel part of MVminx should be no greater than atarget difference for the x coordinate direction, and the integer-pixelpart of MVmaxy and the integer-pixel part of MVminy should be no greaterthan a target difference for the y coordinate direction.

In one example, (MVmaxx, MVmaxy) and (MVminx, MVminy) are determined bya particular one, single sub-block in the M×N block area, such as thefirst sub-block according to a decoding order. The motion vector of thefirst sub-block is denoted as (MVx1, MVy1). In some embodiments,(MVmaxx, MVmaxy) can be set to the maximum values that have the sameinteger value as (MVx1, MVy1), such as

((((MVx1>>MV_precision)+1)<<MV_precision)−1,(((MVy1>>MV_precision)+1)<<MV_precision)−1).

(MVminx, MVminy) can be set to (MVmaxx— T, MVmaxy— T), where T is anoffset value determined according to the target difference by

T=((target difference+1)<<MV_precision)−1,

wherein MV_precision indicates that the motion vector components and Tare expressed in a unit 2^(MV_precision) per pixel. For example, whenthe target difference is 1 pixel, MV_precision is 4, i.e., 1/16-pelprecision, T is 31.

In another example, (MVmaxx, MVmaxy) and (MVminx, MVminy) are determinedby the first sub-block in the M×N block area. (MVminx, MVminy) can beset to the minimum values that have the same integer value as (MVx1,MVy1), such as

(MVx1>>MV_precision<<MV_precision, MVy1>>MV_precision<<MV_precision).

(MVmaxx, MVmaxy) can be set to (MVminx+T, MVminy+T), and T can bedetermined as described above.

In another example, (MVmaxx, MVmaxy) and (MVminx, MVminy) are determinedby more than one sub-blocks in the M×N block area, such as allsub-blocks in the M×N block area. The i-th motion vector of the i-thsub-block is denoted as (MVxi, MVyi). In some embodiments, (MVmaxx,MVmaxy) can be set to (int(max{MVxi})+(1<<MV_precision)−1, int(max{MVyi})+(1<<MV_precision)−1), and (MVminx, MVminy) can be set to be(MVmaxx−T, MVmaxy−T). T can be determined as described above. Also,int(d) represents the integer-pixel part of d. For example, int(d) maybe determined by

int(d)=(d>>MV_precision)<<MV_precision.

In another example, (MVmaxx, MVmaxy) and (MVminx, MVminy) are determinedby more than one sub-blocks in the M×N block area, such as allsub-blocks in the M×N block area. In some embodiments, (MVminx, MVminy)can be set to (int(min{MVxi}), int(min{MVyi})), and (MVmaxx, MVmaxy) canbe set to be (MVminx+T, MVminy+T). T can be determined as describedabove.

In some embodiments, in one example, (MVmaxx, MVmaxy) and (MVminx,MVminy) can be determined by one or more particular sub-blocks in theM×N block area other than just the first sub-block or all sub-blocks asdescribed above. For example, (MVmaxx, MVmaxy) and (MVminx, MVminy) canbe determined by the first two sub-blocks in the M×N block areaaccording to a decoding order or one or more sub-blocks at one or morepredetermined positions in the M×N block area. In some examples, one ofthe sets of upper bounds or lower bounds can be set according to thecorresponding maximum or minimum values of the motion vectors of the oneor more particular sub-blocks, and the other one of the sets of upperbounds or lower bounds can be set according to the value T as describedabove.

In some embodiments, the motion vector adjustment process describedherein can be applied to all sub-block based prediction modes. In someembodiments, the motion vector adjustment process described herein canbe applied to only one or more selected sub-block based predictionmodes. In one example, the motion vector adjustment process describedherein can be applied only to affine blocks. In one example, the motionvector adjustment process described herein can be applied only to planarMV prediction mode. In one example, the motion vector adjustment processdescribed herein can be applied to both affine and SbTMVP but not toplanar MV prediction.

In some embodiments, the target difference can be different for the xcoordinate direction component can be different from the targetdifference for the y coordinate direction component. In one example,when W=4, H>4, and the sub-block size is 4×4. The target difference forhorizontal component (i.e., the x coordinate direction component) of asub-block MV is 1 pixel and the target difference for vertical component(i.e., the y coordinate direction component) of sub-block MV is 2pixels. In one example, when W>4, H=4, and the sub-block size is 4×4,the target difference for horizontal component (i.e., the x coordinatedirection component) of a sub-block MV is 2 pixels and the targetdifference for vertical component (i.e., the y coordinate directioncomponent) of sub-block MV is 1 pixel.

In some embodiments, the motion vector adjustment process describedherein can also be applicable to regular blocks in order to reduce thememory bandwidth requirement for blocks with a smaller size, such as a4×4, 4×8, or 8×4 bi-directional predicted CU, which is not coded using asub-block based prediction mode. In such examples, the motion vectors ofa group of blocks may be constrained so that the absolute differencebetween the integer-pixel part of the motion vector of a current CU(CU_curr) along a particular coordinate direction and the integer-pixelpart of the motion vector of a last inter coded CU (CU_inter_prev) alonga particular coordinate direction is not greater than a targetdifference.

For the regular block application, in some embodiments, the targetdifference can be a fixed value, such as 1 pixel, regardless of a blocksize. In some embodiments, the target difference can be different fordifferent block sizes, such as 1 pixel for 4×4 blocks, and 2 pixels for8×4 or 4×8 blocks. In some embodiments, the target difference for the xcoordinate direction component can be different from the targetdifference for the y coordinate direction component. In someembodiments, the target difference information may be signaled in abitstream, such as in SPS, PPS, a slice header, a tile header, videousage information (VUI), or a supplemental enhancement information (SEI)message.

In one embodiment, if the last inter coded CU is not a spatialneighboring CU of the current CU, and the size of current CU is below athreshold, such as smaller than 8×8, the current CU may not be allowedto be coded using bi-directional prediction.

In some embodiments, the adjusted motion vectors of the sub-blocks (oralso referred to as the target motion vectors of the sub-blocks) thatare adjusted according to a motion vector adjustment process describedherein may not be written back to a motion field. If a target motionvector of a sub-block is not written back to the motion field, thetarget motion vector can be used only for generating prediction samplesfor the sub-block. However, other modules in the video coding device,such as MV prediction and deblocking, can use the base motion vector (orthe motion vector determined before adjustment described in thisdisclosure).

In some embodiments, the adjusted motion vectors of the sub-blocks (orthe target motion vectors of the sub-blocks) may be written back to themotion field. If a target motion vector of a sub-block is written backto the motion field, other modules, such as MV prediction anddeblocking, can use the target motion vector.

In some embodiments, whether to write back the target motion vector tothe motion field may be predefined or signaled in a bitstream, such asin SPS, PPS, a slice header, a tile header, video usage information(VUI), or a supplemental enhancement information (SEI) message.

In some embodiments, in an affine inter mode and/or affine merge mode,the motion vectors of the control points from the spatial neighboringblocks are used in a MV prediction process. If the target sub-blockMV(s) is written back to the motion field, the motion vectors used in MVprediction process according to the affine inter and merge modes are notthe base motion vectors of the control points. In this case, the codingefficiency loss is big.

In some examples, for a W×H inter block which is coded using an affineinter or affine merge mode, the motion vectors corresponding to thetop-left, top-right, and/or bottom-left sub-blocks can be used ascontrol points for the affine inter or affine merge mode and thus can bekept unchanged regardless of the determined (MVmaxx, MVmaxy) and(MVminx, MVminy). In some embodiments, other sub-blocks inside an M×Nblock area (M<=W, N<=H) can still be adjusted according to one or moreadjustment processes as described above, such that a difference ofinteger-pixel parts thereof along the x coordinate direction is equal toor less than a target difference for the x coordinate direction; and adifference of integer-pixel parts thereof along the y coordinatedirection is equal to or less than a target difference for the ycoordinate direction.

In some examples, only one control point sub-block has its motion vector(MVxcp1, MVycp1) kept unchanged. In one example, after determining the(MVmaxx, MVmaxy) and (MVminx, MVminy) as described above, if MVxcp1 islarger than MVmaxx, then MVminx can be changed to(int(MVxcp1)−(threshold<<MV_precision)), and MVmaxx can be changed to(MVminx+T). In one example, if MVycp1is larger than MVmaxy, then MVminycan be changed to (int(MVycp1)−(threshold<<MV_precision)), and MVmaxycan be changed to (MVminy+T). T can be determined as described above.

In one example, if W is 8, H is 8, and a sub-block size is 4×4, the(MVminx, MVmaxx) and (MVminy, MVmaxy) can be determined according to(MVxcp1, MVycp1). After the (MVminx, MVmaxx) and (MVminy, MVmaxy) aredetermined according to (MVxcp1, MVycp1), the upper and lower bounds canbe used for clipping (or adjusting by truncation) the motion vectors ofall sub-blocks in the 8×8 block area.

In some examples, two control point sub-blocks have their motion vectors(MVxcp1, MVycp1) and (MVxcp2, MVycp2) kept unchanged. In one example,the top-left sub-block MV and top-right sub-block MV are kept unchangedduring the sub-block MV adjustment process. In one example, the top-leftsub-block MV and bottom-left sub-block MV are kept unchanged during thesub-block MV adjustment process. In one example, the top-right sub-blockMV and bottom-left sub-block MV are kept unchanged during the sub-blockMV adjustment process. In these examples, for each M×N block areacontaining control point sub-block, the corresponding upper and lowerbounds (MVminx, MVmaxx) and (MVminy, MVmaxy) can be determined accordingto the corresponding motion vector (MVxcp1, MVycp1) or (MVxcp2, MVycp2)that is within the sub-block and is kept unchanged.

In some examples, three control point sub-blocks have their motionvectors (MVxcp1, MVycp1), (MVxcp2, MVycp2), and (MVxcp3, MVycp3) keptunchanged. In these examples, for each M×N block area containing controlpoint sub-block, the corresponding upper and lower bounds (MVminx,MVmaxx) and (MVminy, MVmaxy) can be determined according to thecorresponding motion vector (MVxcp1, MVycp1), (MVxcp2, MVycp2), or(MVxcp3, MVycp3) that is within the sub-block and is kept unchanged.

In some embodiments, the adjusted motion vectors of the sub-blocks (orthe target motion vectors of the sub-blocks) may be written back to themotion field. If a target motion vector of a sub-block is written backto the motion field, other modules, such as MV prediction anddeblocking, can use the target motion vector.

In some embodiments, in an affine inter mode and/or affine merge mode,the motion vectors of the control points from the spatial neighboringblocks are used in a MV prediction process. If the target sub-blockMV(s) is written back to the motion field, the motion vectors used in MVprediction process according to the affine inter and merge modes are notthe base motion vectors of the control points. In this case, the codingefficiency loss is big.

In some embodiments, for an affine block, when constraining sub-blockMVs in an M×N region to have the same integer part of MVs, the motionvector adjustment process may be modified for improved efficiency asfurther described below.

In some embodiments, for an M×N block area, an i-th motion vector of ani-th sub-block can be denoted as (MVxi, MVyi), and (MVminx, MVminy) and(MVmaxx, MVmaxy) can be determined based on the positions of max{MVxi},max{MVyi}, min{MVxi}, and min{MVyi} with respect to the integer-pixelparts thereof. Because the process may be applicable to the x coordinatedirection components and y coordinate direction components in a similarapproach, the following pseudo code example is based on the x coordinatedirection components:

 MVminx = min{MVxi}; // get minimum MV component of sub-block MVs of thetarget reference list along a first coordinate direction (e.g., xcoordinate direction)  MVmaxx = max{MVxi}; // get maximum MV componentof sub-block MVs of the target reference list along the first coordinatedirection (e.g., x coordinate direction)  roundMVminx = MVminx »MV_precision << MV_precision; // get integer part of MVminx  roundMVmaxx= MVmaxx » MV_precision « MV_precision; // get integer part of MVmaxx if ((MVminx - roundMVminx) < (MVmaxx - roundMVmaxx))  {// mainly usemin{MVxi} for the clipping process when min{MVxi} is closer to anroundMVminx   MVminx = roundMVminx;   MVmaxx = MVminx + T; // T is theoffice value as described above  }  else  {// mainly use max{MVxi} forthe clipping process when max{MVxi} is closer to roundMVmaxx   MVmaxx =roundMVmaxx;   MVminx = MVmaxx - T; // T is the office value asdescribed above  }

Therefore, the determining the range of the target motion vectors forthe group of blocks along a particular coordinate direction includedetermining a maximum value of the base motion vectors, along the firstcoordinate direction, for the group of blocks, and determining a minimumvalue of the base motion vectors, along the first coordinate direction,for the group of blocks. In response to a determination that a firstdifference between the minimum value and a first integer-pixel part ofthe minimum value is less than a second difference between the maximumvalue and a second integer-pixel part of the maximum value, the lowerbound value of the range can be determined according to the minimumvalue of the base motion vectors, and the upper bound value of the rangecan be determined according to an integer-pixel portion of thedetermined lower bound value, the target difference, and a precisionsetting of the target motion vectors. Also, in response to adetermination that the first difference is not less than the seconddifference, the upper bound value of the range can be determinedaccording to the maximum value of the base motion vectors, and the lowerbound value of the range can be determined according to an integer-pixelportion of the determined upper bound value, the target difference, andthe precision setting of the target motion vectors.

In some embodiments, the process for the y coordinate directioncomponents can be performed in a manner similar to the pseudo codeexample illustrated above, with the x coordinate direction relatedparameters replaced with y coordinate direction related parameters.

In some embodiments, the target difference for the x coordinatedirection components can be different from the target difference for they coordinate direction components. In one example, the same targetdifference is used for x coordinate direction components and ycoordinate direction components. In one example, the target differencefor both x coordinate direction components and y coordinate directioncomponents is set to 0. In one example, the target difference for xcoordinate direction component is set to 1, and the target differencefor y coordinate direction components is set to 0.

In some embodiments, the sub-block MV adjustment processes described inthis disclosure may be applicable when a block or a block area isbi-directional predicted. In at least one embodiment, the sub-block MVadjustment processes described in this disclosure may be applicable onlywhen a block or a block area is bi-directional predicted ormulti-hypothesis predicted using an affine mode.

Moreover, sub-block MV adjustment processes described in this disclosuremay be implemented by hard-wire circuitry, processing circuitry (e.g.,one or more processors or one or more integrated circuits) executing aset of instructions, or a combination thereof. In one example, the oneor more processors can execute the set of instructions that is stored ina non-transitory computer-readable medium.

FIG. 11 is a flow chart outlining a process (1100) of reconstructing agroup of blocks based on target motion vectors that comply with a set ofconstraints in accordance with one embodiment. The block in this flowchart can refer to a regular block or a sub-block. In some embodiments,one or more operations are performed before or after process (1100), andsome of the operations illustrated in FIG. 11 may be reordered oromitted.

In various embodiments, the process (1100) is executed by processingcircuitry, such as the processing circuitry in the terminal devices(210), (220), (230), and (240), the processing circuitry that performsfunctions of the video decoder (310), (410), or (710), the processingcircuitry that performs functions of the video encoder (303), (503), or(603), and the like. In some embodiments, the process (1100) isimplemented by software instructions, thus when the processing circuitryexecutes the software instructions, the processing circuitry performsthe process (1100). The process starts at (S1110).

At (S1110), motion information of a group of blocks in a picture isobtained from a coded video bitstream. The motion information indicatesbase motion vectors for the group of blocks, and the base motion vectorspoint to a first reference picture in a first prediction list. In someembodiments, the group of blocks includes sub-blocks of a coding blockin the picture. In some embodiments, the first target difference can bedetermined according to a size and a shape of the coding block. In someembodiments, the group of blocks includes regular blocks.

In some embodiments, the first target difference ranges from 0 to 3integer pixels. In some embodiments, the first target difference can bederived according to a video coding standard or signaled via the codedvideo bitstream, such as in a sequence parameter set (SPS) header, apicture parameter set (PPS) header, a slice header, a tile header, videousage information (VUI), or a supplemental enhancement information (SEI)message of the coded video bitstream.

At (S1120), a first range of target motion vectors for the group ofblocks along a first coordinate direction (e.g., the x coordinatedirection or the horizontal direction) can be determined according tothe base motion vectors and a first target difference for the firstcoordinate direction. As such, for any two motion vector within thefirst range, a difference of integer-pixel parts thereof along the firstcoordinate direction is equal to or less than the first targetdifference. The first range can be determined according to one or moremotion vector adjustment processes as described above.

In some embodiments, the determining the first range of the targetmotion vectors for the group of blocks along the first coordinatedirection includes determining one of an upper bound value and a lowerbound value of the first range according to one or more base motionvectors for one or more particular blocks in the group of blocks, theone or more particular blocks corresponding to a respective one or morepredetermined positions in the coding block. The other one of the upperbound value and the lower bound value of the first range can bedetermined according to the determined one of the upper bound value andan integer-pixel portion of the lower bound value, the first targetdifference, and a precision setting of the target motion vectors.

In some embodiments, the one or more particular blocks consist of afirst block in the group of blocks according to a scanning order. Insome embodiments, the one or more particular blocks consist of the firsttwo blocks in the group of blocks according to a scanning order. In someembodiments, the one or more particular blocks include all sub-blocks inthe group of blocks.

In some embodiments, the determining the first range of the targetmotion vectors for the group of blocks along the first coordinatedirection includes determining the upper bound value of the first rangeaccording to a maximum value of the base motion vectors, along the firstcoordinate direction, for the group of blocks. In some embodiments, thedetermining the first range of the target motion vectors for the groupof blocks along the first coordinate direction includes determining thelower bound value of the first range according to a minimum value of thebase motion vectors, along the first coordinate direction, for the groupof blocks.

In some embodiments, the determining the first range of the targetmotion vectors for the group of blocks along the first coordinatedirection includes determining a maximum value of the base motionvectors, along the first coordinate direction, for the group of blocks,and determining a minimum value of the base motion vectors, along thefirst coordinate direction, for the group of blocks. In response to adetermination that a first difference between the minimum value and afirst integer-pixel part of the minimum value is less than a seconddifference between the maximum value and a second integer-pixel part ofthe maximum value, the lower bound value of the first range can beaccording to the minimum value of the base motion vectors, and the upperbound value of the first range can be determined according to aninteger-pixel portion of the determined lower bound value, the firsttarget difference, and a precision setting of the target motion vectors.In response to a determination that the first difference is not lessthan the second difference, the upper bound value of the first range canbe determined according to the maximum value of the base motion vectors,and the lower bound value of the first range can be determined accordingto an integer-pixel portion of the determined upper bound value, thefirst target difference, and the precision setting of the target motionvectors.

At (S1130), a second range of target motion vectors for the group ofblocks along a second coordinate direction (e.g., the y coordinatedirection or the horizontal direction) can be determined according tothe base motion vectors and a second target difference for the secondcoordinate direction. As such, for any two motion vector within thesecond range, a difference of integer-pixel parts thereof along thesecond coordinate direction is equal to or less than the second targetdifference. The second range can be determined according to one or moremotion vector adjustment processes as described above and in a mannersimilar to the process for determining the first range along the firstcoordinate direction.

At (S1140), the base motion vectors of the group of blocks can beconverted into the target motion vectors according to the first rangeand/or the second range. In some embodiments, the converting the basemotion vectors into the target motion vectors includes clipping a firstvalue of a base motion vector, along the first coordinate direction forexample, for a block in the group of blocks to the lower bound valuewhen the first value is less than the lower bound value; and clippingthe first value to the upper bound value when the first value is greaterthan the upper bound value.

In some embodiments, the converting the base motion vectors into thetarget motion vectors includes keeping unchanged, regardless of thefirst range, at least one of three motion vectors for three blocks thatcorrespond to a top-left sub-block, a top-right sub-block, and abottom-left sub-block of the coding block in the picture.

At (S1150), reconstructed samples of the group of blocks are generatedfor output based on the target motion vectors. In some embodiments,after S1150, the base motion vectors for the group of blocks can bestored in a motion filed as reference information for a subsequentmotion vector prediction process or a subsequent deblocking process.

After (S1150), the process terminates.

The techniques described above, can be implemented as computer softwareusing computer-readable instructions and physically stored in one ormore computer-readable media. For example, FIG. 12 shows a computersystem (1200) suitable for implementing certain embodiments of thedisclosed subject matter.

The computer software can be coded using any suitable machine code orcomputer language, that may be subject to assembly, compilation,linking, or like mechanisms to create code comprising instructions thatcan be executed directly, or through interpretation, micro-codeexecution, and the like, by one or more computer central processingunits (CPUs), Graphics Processing Units (GPUs), and the like.

The instructions can be executed on various types of computers orcomponents thereof, including, for example, personal computers, tabletcomputers, servers, smartphones, gaming devices, internet of thingsdevices, and the like.

The components shown in FIG. 12 for computer system (1200) are exemplaryin nature and are not intended to suggest any limitation as to the scopeof use or functionality of the computer software implementingembodiments of the present disclosure. Neither should the configurationof components be interpreted as having any dependency or requirementrelating to any one or combination of components illustrated in theexemplary embodiment of a computer system (1200).

Computer system (1200) may include certain human interface inputdevices. Such a human interface input device may be responsive to inputby one or more human users through, for example, tactile input (such as:keystrokes, swipes, data glove movements), audio input (such as: voice,clapping), visual input (such as: gestures), olfactory input (notdepicted). The human interface devices can also be used to capturecertain media not necessarily directly related to conscious input by ahuman, such as audio (such as: speech, music, ambient sound), images(such as: scanned images, photographic images obtain from a still imagecamera), video (such as two-dimensional video, three-dimensional videoincluding stereoscopic video).

Input human interface devices may include one or more of (only one ofeach depicted): keyboard (1201), mouse (1202), trackpad (1203), touchscreen (1210), data-glove (not shown), joystick (1205), microphone(1206), scanner (1207), camera (1208).

Computer system (1200) may also include certain human interface outputdevices. Such human interface output devices may be stimulating thesenses of one or more human users through, for example, tactile output,sound, light, and smell/taste. Such human interface output devices mayinclude tactile output devices (for example tactile feedback by thetouch-screen (1210), data-glove (not shown), or joystick (1205), butthere can also be tactile feedback devices that do not serve as inputdevices), audio output devices (such as: speakers (1209), headphones(not depicted)), visual output devices (such as screens (1210) toinclude CRT screens, LCD screens, plasma screens, OLED screens, eachwith or without touch-screen input capability, each with or withouttactile feedback capability—some of which may be capable to output twodimensional visual output or more than three dimensional output throughmeans such as stereographic output; virtual-reality glasses (notdepicted), holographic displays and smoke tanks (not depicted)), andprinters (not depicted).

Computer system (1200) can also include human accessible storage devicesand their associated media such as optical media including CD/DVD ROM/RW(1220) with CD/DVD or the like media (1221), thumb-drive (1222),removable hard drive or solid state drive (1223), legacy magnetic mediasuch as tape and floppy disc (not depicted), specialized ROM/ASIC/PLDbased devices such as security dongles (not depicted), and the like.

Those skilled in the art should also understand that term “computerreadable media” as used in connection with the presently disclosedsubject matter does not encompass transmission media, carrier waves, orother transitory signals.

Computer system (1200) can also include an interface to one or morecommunication networks. Networks can for example be wireless, wireline,optical. Networks can further be local, wide-area, metropolitan,vehicular and industrial, real-time, delay-tolerant, and so on. Examplesof networks include local area networks such as Ethernet, wireless LANs,cellular networks to include GSM, 3G, 4G, 5G, LTE and the like, TVwireline or wireless wide area digital networks to include cable TV,satellite TV, and terrestrial broadcast TV, vehicular and industrial toinclude CANBus, and so forth. Certain networks commonly require externalnetwork interface adapters that attached to certain general purpose dataports or peripheral buses (1249) (such as, for example USB ports of thecomputer system (1200)); others are commonly integrated into the core ofthe computer system (1200) by attachment to a system bus as describedbelow (for example Ethernet interface into a PC computer system orcellular network interface into a smartphone computer system). Using anyof these networks, computer system (1200) can communicate with otherentities. Such communication can be uni-directional, receive only (forexample, broadcast TV), uni-directional send-only (for example CANbus tocertain CANbus devices), or bi-directional, for example to othercomputer systems using local or wide area digital networks. Certainprotocols and protocol stacks can be used on each of those networks andnetwork interfaces as described above.

Aforementioned human interface devices, human-accessible storagedevices, and network interfaces can be attached to a core (1240) of thecomputer system (1200).

The core (1240) can include one or more Central Processing Units (CPU)(1241), Graphics Processing Units (GPU) (1242), specialized programmableprocessing units in the form of Field Programmable Gate Areas (FPGA)(1243), hardware accelerators for certain tasks (1244), and so forth.These devices, along with Read-only memory (ROM) (1245), Random-accessmemory (1246), internal mass storage such as internal non-useraccessible hard drives, SSDs, and the like (1247), may be connectedthrough a system bus (1248). In some computer systems, the system bus(1248) can be accessible in the form of one or more physical plugs toenable extensions by additional CPUs, GPU, and the like. The peripheraldevices can be attached either directly to the core's system bus (1248),or through a peripheral bus (1249). Architectures for a peripheral businclude PCI, USB, and the like.

CPUs (1241), GPUs (1242), FPGAs (1243), and accelerators (1244) canexecute certain instructions that, in combination, can make up theaforementioned computer code. That computer code can be stored in ROM(1245) or RAM (1246). Transitional data can be also be stored in RAM(1246), whereas permanent data can be stored for example, in theinternal mass storage (1247). Fast storage and retrieve to any of thememory devices can be enabled through the use of cache memory, that canbe closely associated with one or more CPU (1241), GPU (1242), massstorage (1247), ROM (1245), RAM (1246), and the like.

The computer readable media can have computer code thereon forperforming various computer-implemented operations. The media andcomputer code can be those specially designed and constructed for thepurposes of the present disclosure, or they can be of the kind wellknown and available to those having skill in the computer software arts.

As an example and not by way of limitation, the computer system havingarchitecture (1200), and specifically the core (1240) can providefunctionality as a result of processor(s) (including CPUs, GPUs, FPGA,accelerators, and the like) executing software embodied in one or moretangible, computer-readable media. Such computer-readable media can bemedia associated with user-accessible mass storage as introduced above,as well as certain storage of the core (1240) that are of non-transitorynature, such as core-internal mass storage (1247) or ROM (1245). Thesoftware implementing various embodiments of the present disclosure canbe stored in such devices and executed by core (1240). Acomputer-readable medium can include one or more memory devices orchips, according to particular needs. The software can cause the core(1240) and specifically the processors therein (including CPU, GPU,FPGA, and the like) to execute particular processes or particular partsof particular processes described herein, including defining datastructures stored in RAM (1246) and modifying such data structuresaccording to the processes defined by the software. In addition or as analternative, the computer system can provide functionality as a resultof logic hardwired or otherwise embodied in a circuit (for example:accelerator (1244)), which can operate in place of or together withsoftware to execute particular processes or particular parts ofparticular processes described herein. Reference to software canencompass logic, and vice versa, where appropriate. Reference to acomputer-readable media can encompass a circuit (such as an integratedcircuit (IC)) storing software for execution, a circuit embodying logicfor execution, or both, where appropriate. The present disclosureencompasses any suitable combination of hardware and software.

APPENDIX A: ACRONYMS

JEM: joint exploration modelVVC: versatile video codingBMS: benchmark set

MV: Motion Vector MVD: Motion Vector Difference MVP: Motion VectorPrediction CAB AC: Context-Adaptive Binary Arithmetic Coding MVP: MotionVector Prediction. ATMVP: Advanced Temporal Motion Vector Prediction

SbTMVP: Sub-block temporal MV prediction

STMVP: Spatial-temporal Motion Vector Prediction TMVP: Temporal MotionVector Prediction

POC: Picture order count

DCTIF: Discrete Cosine Transform Interpolation Filter MRSAD: MeanReduced Sum of Average Difference

DMVD: decoder side motion vector derivationDMVR: Decoder side motion vector refinementVTM: Versatile Video Coding test model

HMVP: History-based Motion Vector Prediction FIFO: First-In-First-OutSPS: Sequence Parameter Set PPS: Picture Parameter Set

SDR: Standard dynamic rangeHDR: high dynamic range

HEVC: High Efficiency Video Coding SEI: Supplementary EnhancementInformation VUI: Video Usability Information GOPs: Groups of PicturesTUs: Transform Units, PUs: Prediction Units CTUs: Coding Tree UnitsCTBs: Coding Tree Blocks PBs: Prediction Blocks HRD: HypotheticalReference Decoder SNR: Signal Noise Ratio CPUs: Central Processing UnitsGPUs: Graphics Processing Units CRT: Cathode Ray Tube LCD:Liquid-Crystal Display OLED: Organic Light-Emitting Diode CD: CompactDisc DVD: Digital Video Disc ROM: Read-Only Memory RAM: Random AccessMemory ASIC: Application-Specific Integrated Circuit PLD: ProgrammableLogic Device LAN: Local Area Network

GSM: Global System for Mobile communications

LTE: Long-Term Evolution CANBus: Controller Area Network Bus USB:Universal Serial Bus PCI: Peripheral Component Interconnect FPGA: FieldProgrammable Gate Areas

SSD: solid-state drive

IC: Integrated Circuit CU: Coding Unit JVET: Joint Video ExplorationTeam

While this disclosure has described several exemplary embodiments, thereare alterations, permutations, and various substitute equivalents, whichfall within the scope of the disclosure. It will thus be appreciatedthat those skilled in the art will be able to devise numerous systemsand methods which, although not explicitly shown or described herein,embody the principles of the disclosure and are thus within the spiritand scope thereof.

What is claimed is:
 1. A method for video encoding in an encoder,comprising: obtaining a current block having a size of W×H pixels andincluding a plurality of sub-blocks according to a sub-block based interprediction mode, the plurality of sub-blocks being arranged into one ormore areas having a size of M×N pixels in the current block, M≤W, andN≤H; for each area of the one or more areas having the size of M×Npixels in the current block: determining base motion vectors of aportion of the sub-blocks within a corresponding area, the portionincluding at least one non-corner sub-block of the current block;converting the base motion vectors of the portion of the sub-blocks intorespective target motion vectors of the portion of the sub-blocks, therespective target motion vectors being confined by a first lower boundand a first upper bound along a first coordinate direction and by asecond lower bound and a second upper bound along a second coordinatedirection, and the converting comprising, for a base motion vector ofthe at least one non-corner sub-block in the portion of the sub-blockswithin the corresponding area, clipping values exceeding one of thefirst lower bound, the first upper bound, the second lower bound, or thesecond upper bound; and encoding samples of the corresponding areaaccording to the target motion vectors of the portion of the sub-blocks;and generating a coded video bitstream including (i) the encoded samplesof each of the one or more areas and (ii) prediction information of thecurrent block, the prediction information indicating the sub block basedinter prediction mode and indicating the base motion vectors of theportion of the subblocks.
 2. The method of claim 1, further comprising,for each area of the one or more areas having the size of M×N pixels inthe current block: determining a first range defined by the first lowerbound and the first upper bound of the target motion vectors of theportion of the sub-blocks along the first coordinate direction; anddetermining a second range defined by the second lower bound and thesecond upper bound of the target motion vectors of the portion of thesub-blocks along the second coordinate direction.
 3. The method of claim2, wherein the converting the base motion vectors of the portion of thesub-blocks into the respective target motion vectors of the portion ofthe sub-blocks comprises, for converting a particular base motion vectorinto a particular target motion vector: clipping a first value of theparticular base motion vector along the first coordinate direction tothe first lower bound of the first range when the first value is lessthan the first lower bound; clipping the first value to the first upperbound of the first range when the first value is greater than the firstupper bound; clipping a second value of the particular base motionvector along the second coordinate direction to the second lower boundof the second range when the second value is less than the second lowerbound; and clipping the second value to the second upper bound of thesecond range when the second value is greater than the second upperbound.
 4. The method of claim 2, wherein the determining the first rangeis performed based on a particular base motion vector of a particularsub-block among the portion of the sub-blocks within the correspondingarea having the size of M×N pixels.
 5. The method of claim 4, whereinthe particular sub-block is a first sub-block in the area according to ascanning order.
 6. The method of claim 2, wherein the determining thefirst range is performed based on all the base motion vectors of theportion of the sub-blocks within the corresponding area.
 7. The methodof claim 2, wherein the determining the first range of the target motionvectors comprises performing one of: determination of the first upperbound of the first range according to a maximum value of the base motionvectors along the first coordinate direction and determination of thefirst lower bound of the first range according to the first upper boundand a target difference; and determination of the first lower bound ofthe first range according to a minimum value of the base motion vectorsalong the first coordinate direction and determination of the firstupper bound of the first range according to the first lower bound andthe target difference.
 8. The method of claim 1, further comprising:setting one or more of three target motion vectors of three cornersub-blocks that correspond to a top-left sub-block, a top-rightsub-block, and a bottom-left sub-block of the current block by keepingcorresponding one or more of three base motion vectors of the threecorner sub-blocks unchanged without performing the converting.
 9. Themethod of claim 7, wherein the target difference is 0, 1, 2, or 3pixels.
 10. The method of claim 1, further comprising: indicating M andN in a sequence parameter set (SPS), a picture parameter set (PPS), or aslice header of the coded video bitstream.
 11. The method of claim 7,wherein the size of M×N pixels is one of: 8×8 pixels, 8×4 pixels, and4×8 pixels.
 12. The method of claim 11, wherein the target difference is1 pixel when the size of M×N pixels is 8×8 pixels, and the targetdifference is 2 pixels when the size of M×N pixels is 8×4 pixels or 4×8pixels.
 13. An apparatus for video decoding, comprising: processingcircuitry configured to: obtain a current block having a size of W×Hpixels and including a plurality of sub-blocks according to a sub-blockbased inter prediction mode, the plurality of sub-blocks being arrangedinto one or more areas having a size of M×N pixels in the current block,M≤W, and N≤H; for each area of the one or more areas having the size ofM×N pixels in the current block: determine base motion vectors of aportion of the sub-blocks within a corresponding area, the portionincluding at least one non-corner sub-block of the current block;convert the base motion vectors of the portion of the sub-blocks intorespective target motion vectors of the portion of the sub-blocks, therespective target motion vectors being confined by a first lower boundand a first upper bound along a first coordinate direction and by asecond lower bound and a second upper bound along a second coordinatedirection, and the converting comprising, for a base motion vector ofthe at least one non-corner sub-block in the portion of the sub-blockswithin the corresponding area, clipping values exceeding one of thefirst lower bound, the first upper bound, the second lower bound, or thesecond upper bound; and encode samples of the corresponding areaaccording to the target motion vectors of the portion of the sub-blocks;and generate a coded video bitstream including (i) the encoded samplesof each of the one or more areas and (ii) prediction information of thecurrent block, the prediction information indicating the sub block basedinter prediction mode and indicating the base motion vectors of theportion of the subblocks.
 14. The apparatus of claim 13, wherein theprocessing circuitry is further configured to, for each area of the oneor more areas having the size of M×N pixels in the current block:determine a first range defined by the first lower bound and the firstupper bound of the target motion vectors of the portion of thesub-blocks along the first coordinate direction; and determine a secondrange defined by the second lower bound and the second upper bound ofthe target motion vectors of the portion of the sub-blocks along thesecond coordinate direction.
 15. The apparatus of claim 14, wherein theprocessing circuitry is further configured to, for converting aparticular base motion vector into a particular target motion vector:clip a first value of the particular base motion vector along the firstcoordinate direction to the first lower bound of the first range whenthe first value is less than the first lower bound; clip the first valueto the first upper bound of the first range when the first value isgreater than the first upper bound; clip a second value of theparticular base motion vector along the second coordinate direction tothe second lower bound of the second range when the second value is lessthan the second lower bound; and clip the second value to the secondupper bound of the second range when the second value is greater thanthe second upper bound.
 16. The apparatus of claim 14, wherein theprocessing circuitry is further configured to perform one of:determination of the first upper bound of the first range according to amaximum value of the base motion vectors along the first coordinatedirection and determination of the first lower bound of the first rangeaccording to the first upper bound and a target difference; anddetermination of the first lower bound of the first range according to aminimum value of the base motion vectors along the first coordinatedirection and determination of the first upper bound of the first rangeaccording to the first lower bound and the target difference.
 17. Theapparatus of claim 13, wherein the processing circuitry is furtherconfigured to: set one or more of three target motion vectors of threecorner sub-blocks that correspond to a top-left sub-block, a top-rightsub-block, and a bottom-left sub-block of the current block by keepingcorresponding one or more of three base motion vectors of the threecorner sub-blocks unchanged without performing the converting.
 18. Theapparatus of claim 16, wherein the target difference is 0, 1, 2, or 3pixels.
 19. The apparatus of claim 13, wherein the processing circuitryis further configured to: indicate M and N in a sequence parameter set(SPS), a picture parameter set (PPS), or a slice header of the codedvideo bitstream.
 20. A non-transitory computer-readable medium storinginstructions which when executed by a computer for video decoding causethe computer to perform: obtaining a current block having a size of W×Hpixels and including a plurality of sub-blocks according to a sub-blockbased inter prediction mode, the plurality of sub-blocks being arrangedinto one or more areas having a size of M×N pixels in the current block,M≤W, and N≤H; for each area of the one or more areas having the size ofM×N pixels in the current block: determining base motion vectors of aportion of the sub-blocks within a corresponding area, the portionincluding at least one non-corner sub-block of the current block;converting the base motion vectors of the portion of the sub-blocks intorespective target motion vectors of the portion of the sub-blocks, therespective target motion vectors being confined by a first lower boundand a first upper bound along a first coordinate direction and by asecond lower bound and a second upper bound along a second coordinatedirection, and the converting comprising, for a base motion vector ofthe at least one non-corner sub-block in the portion of the sub-blockswithin the corresponding area, clipping values exceeding one of thefirst lower bound, the first upper bound, the second lower bound, or thesecond upper bound; and encoding samples of the corresponding areaaccording to the target motion vectors of the portion of the sub-blocks;and generating a coded video bitstream including (i) the encoded samplesof each of the one or more areas and (ii) prediction information of thecurrent block, the prediction information indicating the sub block basedinter prediction mode and indicating the base motion vectors of theportion of the subblocks.